The present invention relates to a novel prosthetic body for bone substitute formed of a sintered porous hydroxyapatite and a method for the preparation thereof.
Along with the progress of the medical engineering in recent years, intensive investigations are now under way for an artificial material of a bone substitute used in the prosthesis of the bones lost by a traffic accident or some diseases such as bone tumors. Such a prosthetic body for bone substitute to be embedded in the human body should of course satisfy various rather difficult requirements that the material has no toxicity to living body to be usable with safety and the mechanical strength thereof should be sufficiently large to approximate the strength of natural bones. In addition, it is desirable that the prosthetic body embedded in the living body can spontaneously disappear to be replaced with the neogenetic bones.
A great variety of artificial materials have been proposed as a prosthetic body for bone substitute although none of them is quite satisfactory in one or more respects, among which hydroxyapatite is one of the most promising prosthetic materials. Hydroxyapatite is a mineral expressed by the chemical formula Ca.sub.10 (PO.sub.4).sub.6.(OH).sub.2 which is the principal constitutent of bones and teeth of vertebrate animals so that the sintered body prepared thereof is promising as a prosthetic body for bone and tooth substitutes by virtue of the affinity thereof to the tissues of human body. Indeed, many investigations have been dedicated to the development of this material for the practical applications thereof as a prosthetic body.
The hitherto developed prosthetic bodies of hydroxyapatite are, however, also not without problems. In order that a prosthetic body embedded in the living body is rapidly and firmly bonded to the tissue of the living body, for example, it is a desirable condition that at least the surface layer of the prosthetic body has a certain degree of porosity so that the living body tissue can enter the pores to anchor the prosthetic body at the position. Such a requirement for porosity of a sintered prosthetic body is incompatible with the requirement for a mechanical strength of the body as large as possible and the mechanical strength of a sufficiently porous sintered body cannot be large enough to ensure its application as a bone substitute. Thus, no prosthetic body with practical applicability has yet been obtained by sintering hydroxyapatite.